The present invention relates to a transfer belt device that transfers a developer image formed on an image bearing member to a recording medium or a transfer belt, and an image forming apparatus provided with this transfer belt device.
In recent years, there has been active development of image forming apparatuses from the two aspects of converting to color and increasing speed. In the colorization of image forming apparatuses, instead of quad-rotational process systems using one image forming station, tandem systems using multiple image forming stations that are able to increase speed have become mainstream.
Tandem image forming apparatuses are provided with a transfer belt device having an endless transfer belt that forms a transport path that transports a recording medium or a developer image, and multiple image forming stations corresponding to each hue arranged in parallel along the transport path, and can perform both color image formation and monochrome (black and white) image formation.
Also, in tandem image forming apparatuses it is possible to set different image forming performance for a color image forming mode that forms color images and for a monochrome image forming mode that forms monochrome images.
For example, there are tandem image forming apparatuses with a configuration wherein the image forming speed is made faster in the monochrome image forming mode, increasing the volume of image formation in monochrome image forming mode. Also, as disclosed in JP 2000-242057A, there are tandem image forming apparatuses with a configuration wherein the diameter of the image bearing member for monochrome images is made larger than the diameter of image bearing members for color images, making the usable time period of the image bearing member for monochrome images equal to that of the image bearing members for color images.
This is because ordinarily, in a single image forming apparatus the frequency of monochrome image formation is higher than that of color image formation. The image bearing member for monochrome images included in the image forming station for monochrome images is used for both color image formation and monochrome image formation, and so its frequency of use is higher than the image bearing members for color images included in the image forming station for color images. Thus, in comparison to the image bearing members for color images, the image bearing member for monochrome images will have a shorter usable time period even if the lifetime is the same.
Accordingly, it is possible to set the specifications for image forming performance, for example changing the speed of image formation in the monochrome image forming mode, for each model of tandem image forming apparatus. Also, in order to set the specifications for image forming performance that differs in each tandem image forming apparatus, specifications are ordinarily set for the color image forming stations and for the monochrome image forming station in each apparatus, and for the transfer belt device, according to the purpose of the image forming apparatus.
On the other hand, the transfer belt device provided in the tandem image forming apparatus is configured from a plurality of rollers that tightly stretch the transfer belt and a transfer unit that supports these multiple rollers. The transfer unit is configured from a plurality of transfer rollers arranged inside the transfer belt. The transfer roller is arranged such that it faces the image bearing member of each image forming station via the transfer belt, and transfers a developer image formed on the surface of the image bearing member of each image forming station onto an outer peripheral surface of the transfer belt or a recording medium transported on the outer peripheral surface of the transfer belt.
Because the transport belt as described above is tightly stretched by the plurality of rollers supported by the transfer unit, work to remove the transfer belt from the transfer unit and exchange it with a new one takes time. Accordingly, in the transfer belt device of recent years, as disclosed in JP H8-69238A and JP 2004-109267A, configurations have been adopted wherein a first transfer unit and a second transfer unit are linked together in the axial direction of the plurality of rollers by a parallel shaft such that they can swing.
Thus, by swinging the first transfer unit or the second transfer unit into a V-shape, the tightly stretched transfer belt loosens and it becomes easy to replace the transfer belt.
However, in the sort of tandem image forming apparatus described above, the image forming stations and the transfer belt device, whose specifications differ for each model of image forming apparatus, are supplied having been respectively designed for each model of image forming apparatus, and so there is the problem of increased manufacturing and assembly costs.
Also, even in a configuration as described above wherein the first transfer unit and second transfer unit are linked together in the axial direction of the plurality of rollers by a parallel shaft such that they can swing, the transfer belt is tightly stretched with the first and second transfer units linked together such that they can swing, but because the transfer units are not configured for use for color images and monochrome images, as stated above the belt apparatus is provided having been designed with varying specifications for each image forming apparatus, and the same problems occur as described above.
It is an object of this invention to provide a transfer belt device configured using a color image transfer unit and a monochrome image transfer unit, wherein an increase in the number of types of parts that accompanies an increase in the number of image forming apparatus models is reduced by achieving an increase in the number of parts shared between a plurality of models, and by also sharing the assembly method, it is possible to achieve model evolution while suppressing an increase in costs; and to provide an image forming apparatus provided with this transfer belt device.